Osteolytic bone disease is a serious complication of common tumors such as breast and lung cancer, causing considerable morbidity such as pain, pathological fracture and hypercalcemia. In some patients with advanced disease, a large component of the tumor burden may be present in the skeleton. Since recent data has shown that the tumor-related peptide PTH-rP is not only responsible for hypercalcemia, but also for osteolytic bone disease in the absence of hypercalcemia, the investigators have identified small molecular weight compounds that inhibit bone metastasis by reducing PTH-rP transcription and expression by tumor cells. Such compounds are candidate drugs for the treatment of osteolytic bone lesions and hypercalcemia occurring in patients with common malignancies. PROPOSED COMMERCIAL APPLICATION: Osteolytic bone disease is a major problem in the cancer population. It causes considerable morbidity and mortality, and once tumor cells become housed in the skeleton, the tumor is non-curable. Our goal is to develop effective drugs which inhibit the major molecular mechanisms responsible for this process, and in particular to evaluate the drug 6-thioguanine used in low doses for this effect.